1. Field of the Invention
The present invention relates in general to fuel gauge systems for measuring the amount of a fuel contained in a container, and more particularly to fuel gauge systems of a type which measures the amount of a mixed fuel, such as a mixture of gasoline and methanol, contained in a fuel tank of a motor vehicle.
2. Description of the Prior Art
In order to clarify the task of the present invention, one conventional fuel gauge system will be outlined with reference to FIG. 5.
In the drawing, designated by numeral 1 is a fuel tank of a motor vehicle, in which a fuel "FX" is contained. A filler cap 8 is detachably connected to a fuel inlet tube of the fuel tank 1. An electric fuel pump 2 is disposed in the fuel tank 1. A fuel supply pipe 3 extends from the pump 2 to a fuel injection valve 5 of an internal combustion engine 4 of the vehicle.
Installed in the fuel tank 1 is a fuel level meter 6 of a float type from which a voltage signal representative of the level of the fuel is fed to a fuel level indicator 7 through a wire (no numeral). Usually, the fuel gauge system is so designed as to make the fuel level indicator 7 point the indicia "EMPTY" when a small amount of fuel is still left in the fuel tank 1. With this, the vehicle can move by a certain distance even after the "EMPTY" indication.
However, the above-mentioned type fuel gauge system suffers the following drawback particularly when it is used for measuring a mixed fuel, such as, a mixture of gasoline and methanol. (Nowadays, for dealing with the air polution problem and energy crisis, such mixed fuel has been proposed and used as the fuel for the motor vehicles.)
That is, as is known to those skilled in the art, due to respective calorific powers possessed by gasoline and methanol, the mileage of the motor vehicle varies considerably depending on the mixing ratio of methanol in the fuel. In fact, the mileage decreases as the mixing ratio of methanol in the fuel increases. This tends to cause an undesired "out of fuel" condition in a motor vehicle when the "EMPTY" indication occurs especially when the vehicle operates on the mixed fuel which contains a large amount of methanol.
In order to solve this drawback, Japanese Utility Model First Provisional Publication No. 62-79113 proposes a measure in which the amount of a mixed fuel is calculated in terms of gasoline. In this measure, the fuel level indicator indicates the calculated amount of the remaining mixed fuel when the same points the indicia "EMPTY".
In this measure, however, a new drawback is encountered. That is, the fuel level indicator can not indicate the amount of the mixed fuel when the fuel tank is filled with the mixed fuel. Thus, it is impossible to recognize the fuel tank being filled with the fuel under fuel feeding of the motor vehicle.